Abnormal cortical processing of voluntary muscle relaxation in patients with focal hand dystonia studied by movement-related potentials

Temporal Signature of Task-Specificity in Isolated Focal Laryngeal Dystonia

BACKGROUND AND OBJECTIVE

Laryngeal dystonia (LD) is focal task-specific dystonia, predominantly affecting speech but not whispering or emotional vocalizations. Prior neuroimaging studies identified brain regions forming a dystonic neural network and contributing to LD pathophysiology. However, the underlying temporal dynamics of these alterations and their contribution to the task-specificity of LD remain largely unknown. The objective of the study was to identify the temporal-spatial signature of altered cortical oscillations associated with LD pathophysiology.

METHODS

We used high-density 128-electrode electroencephalography (EEG) recordings during symptomatic speaking and two asymptomatic tasks, whispering and writing, in 24 LD patients and 22 healthy individuals to investigate the spectral dynamics, spatial localization, and interregional effective connectivity of aberrant cortical oscillations within the dystonic neural network, as well as their relationship with LD symptomatology.

RESULTS

Symptomatic speaking in LD patients was characterized by significantly increased gamma synchronization in the middle/superior frontal gyri, primary somatosensory cortex, and superior parietal lobule, establishing the altered prefrontal-parietal loop. Hyperfunctional connectivity from the left middle frontal gyrus to the right superior parietal lobule was significantly correlated with the age of onset and the duration of LD symptoms. Asymptomatic whisper in LD patients had not no statistically significant changes in any frequency band, whereas asymptomatic writing was characterized by significantly decreased synchronization of beta-band power localized in the right superior frontal gyrus.

CONCLUSION

Task-specific oscillatory activity of prefrontal-parietal circuitry is likely one of the underlying mechanisms of aberrant heteromodal integration of information processing and transfer within the neural network leading to dystonic motor output. © 2023 International Parkinson and Movement Disorder Society.

Neurophysiological Basis of Deep Brain Stimulation and Botulinum Neurotoxin Injection for Treating Oromandibular Dystonia

Oromandibular dystonia (OMD) induces severe motor impairments, such as masticatory disturbances, dysphagia, and dysarthria, resulting in a serious decline in quality of life. Non-invasive brain-imaging techniques such as electroencephalography (EEG) and magnetoencephalography (MEG) are powerful approaches that can elucidate human cortical activity with high temporal resolution. Previous studies with EEG and MEG have revealed that movements in the stomatognathic system are regulated by the bilateral central cortex. Recently, in addition to the standard therapy of botulinum neurotoxin (BoNT) injection into the affected muscles, bilateral deep brain stimulation (DBS) has been applied for the treatment of OMD. However, some patients' OMD symptoms do not improve sufficiently after DBS, and they require additional BoNT therapy. In this review, we provide an overview of the unique central spatiotemporal processing mechanisms in these regions in the bilateral cortex using EEG and MEG, as they relate to the sensorimotor functions of the stomatognathic system. Increased knowledge regarding the neurophysiological underpinnings of the stomatognathic system will improve our understanding of OMD and other movement disorders, as well as aid the development of potential novel approaches such as combination treatment with BoNT injection and DBS or non-invasive cortical current stimulation therapies.

Modulation of sensorimotor cortical oscillations in athletes with yips

The yips, an involuntary movement impediment that affects performance in skilled athletes, is commonly described as a form of task-specific focal dystonia or as a disorder lying on a continuum with focal dystonia at one end (neurological) and chocking under pressure at the other (psychological). However, its etiology has been remained to be elucidated. In order to understand sensorimotor cortical activity associated with this movement disorder, we examined electroencephalographic oscillations over the bilateral sensorimotor areas during a precision force task in athletes with yips, and compared them with age-, sex-, and years of experience-matched controls. Alpha-band event-related desynchronization (ERD), that occurs during movement execution, was greater in athlete with yips as compared to controls when increasing force output to match a target but not when adjusting the force at around the target. Event-related synchronization that occurs after movement termination was also greater in athletes with yips. There was no significant difference in task performance between groups. The enhanced ERD is suggested to be attributed to dysfunction of inhibitory system or increased allocation of attention to the body part used during the task. Our findings indicate that sensorimotor cortical oscillatory response is increased during movement initiation in athletes with yips.

MRCP as a biomarker of motor action with varying degree of central and peripheral contribution as defined by ultrasound imaging

Motor imagination is an alternative rehabilitation strategy for people who cannot execute real movements. However, it is still a matter of debate to which degree it involves activation of deeper muscle structures, which cannot be detected by surface electromyography (SEMG). Sixteen able-bodied participants performed cue based isometric ankle plantar flexion (active movement) followed by active relaxation under four conditions: executed movements with two levels of muscle contraction (fully executed and attempted movements, EM and AM) and motor imagination with and without detectable muscle twitches (IT and I). The most prominent peaks and distinctive phases of movement-related cortical potential (MRCP) were compared between conditions. Ultrasound imaging (USI) and SEMG were used to detect movements. IT showed spatially distinctive significant differences compared to both I and AM during active movement preparation and reafferentation phase; further widespread differences were found between IT and AM during active movement execution and posteriorly during preparation for active relaxation. EM and AM showed the largest differences frontally during active movement planning and posteriorly during execution of active relaxation. Movement preparation positivity P1 showed a significant difference in amplitude between IT and AM but not between IT and I. USI can detect subliminal movements (twitches) better than SEMG. MRCP is a biomarker sensitive to different levels of muscle contraction and relaxation. IT is a motor condition distinguishable from both I and AM. EEG biomarkers of movements could be used to identify pathological conditions, that manifest themselves during either active contraction or active relaxation.NEW & NOTEWORTHY Ultrasound imaging can detect subtle muscle movements (twitches) that are not detectable with electromyography. Almost a quarter of trials of imagined movements in able-bodied people are accompanied by twitches. Analysis of movement-related cortical potential showed that motor imagination with twitches is a condition distinguishable from motor imagination without twitches and from motor attempts.

Change in motor cortex activation for muscle release by motor learning

For central nervous system disorders' rehabilitation, it is important to accurately understand motor control and implement an appropriate motor learning process to induce neuroplastic changes. The neurophysiological studies have revealed that neural control mechanisms are crucial during both the onset of muscular activities and muscle release after contraction. When performing various movements during daily activities, muscle relaxation control enables precise force output and timing control. Moreover, surround inhibition is a functional mechanism in the motor system. Surround inhibition of the motor system may be involved in the selective execution of desired movements. This review demonstrates cortical excitability resulting from motor learning, movement control mechanisms including muscle relaxation and the suppression of nontarget muscle groups, and the voluntary drive's importance that is required for movement.

Voluntary Muscle Relaxation Can Mitigate Fatigue and Improve Countermovement Jump Performance

Pinto, BL and McGill, SM. Voluntary muscle relaxation can mitigate fatigue and improve countermovement jump performance. J Strength Cond Res 34(6): 1525-1529, 2020-When muscles contract, they create force and stiffness. Thus, muscle activation and relaxation must be strategically sequenced to coordinate and control movement, to enhance athletic variables such as speed and strength. However, research has favored investigation of muscle activation over relaxation. Athletes such as runners, swimmers, and boxers often shake their limbs to allow the muscle to oscillate freely, immediately before a bout. The purpose was to investigate whether shaking the lower limbs with the intention to voluntarily relax the muscles of the limb has an effect on countermovement jump (CMJ) performance. Subjects performed 10 maximal effort CMJs with 30 seconds of rest between each jump. During the rest period, they either performed the relaxation technique or control condition (standing still). Statistical significance was considered at p < 0.05. Subjects significantly improved jump height, compared with their first jump of the day, when performing the relaxation technique. To further investigate the mechanism of enhancement, subjects were grouped into responders and nonresponders. The responder group significantly decreased their jump height and concentric phase impulse (relative to the first jump) during the control condition compared with the nonresponder group, indicating fatigue. When performing the relaxation technique, the responder group improved their jump height and mitigated fatigue by significantly increasing their unweighting impulse and unweighting force. The relaxation technique improved CMJ performance, specifically in those that fatigue with consecutive bouts, by enhancing unweighting, that requires muscle relaxation, rather than propulsion that requires activation. This technique can be useful for training or competition.

On Stopping Voluntary Muscle Relaxations and Contractions: Evidence for Shared Control Mechanisms and Muscle State-Specific Active Breaking

Control of the body requires inhibiting complex actions, involving contracting and relaxing muscles. However, little is known of how voluntary commands to relax a muscle are cancelled. Action inhibition causes both suppression of muscle activity and the transient excitation of antagonist muscles, the latter being termed active breaking. We hypothesized that active breaking is present when stopping muscle relaxations. Stop signal experiments were used to compare the mechanisms of active breaking for muscle relaxations and contractions in male and female human participants. In experiments 1 and 2, go signals were presented that required participants to contract or relax their biceps or triceps muscle. Infrequent Stop signals occurred after fixed delays (0-500 ms), requiring that participants cancelled go commands. In experiment 3, participants increased (contract) or decreased (relax) an existing isometric finger abduction depending on the go signal, and cancelled these force changes whenever Stop signals occurred (dynamically adjusted delay). We found that muscle relaxations were stopped rapidly, met predictions of existing race models, and had Stop signal reaction times that correlated with those observed during the stopping of muscle contractions, suggesting shared control mechanisms. However, stopped relaxations were preceded by transient increases in electromyography (EMG), while stopped contractions were preceded by decreases in EMG, suggesting a later divergence of control. Muscle state-specific active breaking occurred simultaneously across muscles, consistent with a central origin. Our results indicate that the later stages of action inhibition involve separate excitatory and inhibitory pathways, which act automatically to cancel complex body movements.SIGNIFICANCE STATEMENT The mechanisms of how muscle relaxations are cancelled are poorly understood. We showed in three experiments involving multiple effectors that stopping muscle relaxations involves transient bursts of EMG activity, which resemble cocontraction and have onsets that correlate with Stop signal reaction time. Comparison with the stopping of matched muscle contractions showed that active breaking was muscle state specific, being positive for relaxations and negative for contractions. The two processes were also observed to co-occur in agonist-antagonist pairs, suggesting separate pathways. The rapid, automatic activation of both pathways may explain how complex actions can be stopped at any stage of their execution.

Brain Activity Underlying Muscle Relaxation

Fine motor control of not only muscle contraction but also muscle relaxation is required for appropriate movements in both daily life and sports. Movement disorders such as Parkinson’s disease and dystonia are often characterized by deficits of muscle relaxation. Neuroimaging and neurophysiological studies suggest that muscle relaxation is an active process requiring cortical activation, and not just the cessation of contraction. In this article, we review the neural mechanisms of muscle relaxation, primarily utilizing research involving transcranial magnetic stimulation (TMS). Several studies utilizing single-pulse TMS have demonstrated that, during the relaxation phase of a muscle, the excitability of the corticospinal tract controlling that particular muscle is more suppressed than in the resting condition. Other studies, utilizing paired-pulse TMS, have shown that the intracortical inhibition is activated just before muscle relaxation. Moreover, muscle relaxation of one body part suppresses cortical activities controlling other body parts in different limbs. Therefore, the cortical activity might not only be a trigger for muscle relaxation of the target muscles but could also bring about an inhibitory effect on other muscles. This spread of inhibition can hinder the appropriate contraction of muscles involved in multi-limb movements such as those used in sports and the play of musical instruments. This may also be the reason why muscle relaxation is so difficult for beginners, infants, elderly, and the cognitively impaired.

Quantitative Assessment of Hand Dysfunction in Patients with Early Parkinson's Disease and Focal Hand Dystonia

Objective

Motor impairments related to hand function are common symptoms in patients with movement disorders, such as Parkinson’s disease (PD) and focal hand dystonia (FHD). However, hand dysfunction has not been quantitatively assessed as a clinical tool for screening patient groups from healthy controls (HCs). The aim of our study was 1) to quantitatively assess hand dysfunction in patients with PD and FHD and its usefulness as a screening tool 2) to grade disease severity in PD and FHD based on hand dysfunction.

Methods

The current case-control study included HCs (n = 50) and patients with known history of PD (n = 25) or FHD (n = 16). Hand function was assessed by a precision grip task while participants lifted objects of 1.3 N and 1.7 N under dry skin conditions, followed by very wet skin conditions (VWSCs). Receiver operating characteristic and summative scoring analyses were performed.

Results

In PD, the combination of loading phase duration and lifting phase duration at quantitative cutoffs of 0.36 and 0.74 seconds identified 21/25 patients as diseased and 49/50 subjects as HCs with 1.7 N under VWSCs. In PD, 5/21 was graded as “mild” and 16/21 as “moderate cases.” In FHD, slip force at a cutoff of 1.2 N identified 13/16 patients as diseased and 41/50 subjects as HC with 1.7 N under VWSCs, but disease severity could not be graded.

Conclusion

Our results demonstrate the use of precision grip task as an important clinical tool in assessment of hand dysfunction in movement disorder patients. Use of quantitative cutoffs may improve diagnostic accuracy and serve as a valuable adjunct to existing clinical assessment methods.

Corticospinal excitability for hand muscles during motor imagery of foot changes with imagined force level

The object of this study was to clarify whether corticospinal excitability controlling hand muscles changes concurrently with increases in the imagined contraction level of foot dorsiflexion. Twelve participants performed actual and imagined dorsiflexion of their right foot at three different EMG levels (10, 40 or 80% of the maximum voluntary contraction). During isometric actual- or imagined- dorsiflexion, transcranial magnetic stimulation (TMS) was delivered to the right hand area of the left primary motor cortex. Motor evoked potentials (MEPs) were recorded from the right extensor carpi radialis (ECR) and flexor carpi radialis (FCR). During actual contraction, MEP amplitudes of ECR and FCR increased with an increased EMG level of dorsiflexion. Similarly, during imagery contraction, MEP amplitudes of ECR and FCR increased with the intensity of imagery contraction. Furthermore, a correlation between MEP amplitude during actual contraction and imagery contraction was observed for both ECR and FCR. Motor imagery of foot contraction induced an enhancement of corticospinal excitability for hand muscles that was dependent on the imagined contraction levels, just as what was observed when there was an actual contraction.

Focal Hand Dystonia Affecting Musicians. Part I: An Overview Of Epidemiology, PathoPhysiology And Medical Treatments

In 1911, Oppenheim coined the term ‘dystonia’ to describe disordered motor control, characterised by an association of hypotonia and tonic muscle spasm. Focal hand dystonia is one form of this disorder, in which symptoms are often task-specific and occur during skilled movements such as writing (writer's cramp) or playing a musical instrument (musician's cramp). Much research has been conducted on the pathophysiology of dystonia, but the underlying mechanisms still remain unclear. Hypotheseses about functional central nervous system alterations continue to gain more support. Scientific treatment-based publications on focal dystonia are sparse, and progress in evidence-based treatment options are necessary in order to assist this patient group. This paper will review the literature, documenting dystonia classification criteria, manifestations, pathophysiology and medical treatment techniques for musicians affected by focal hand dystonia.

Muscle Relaxation of the Foot Reduces Corticospinal Excitability of Hand Muscles and Enhances Intracortical Inhibition

The object of this study was to clarify the effects of foot muscle relaxation on activity in the primary motor cortex (M1) of the hand area. Subjects were asked to volitionally relax the right foot from sustained contraction of either the dorsiflexor (tibialis anterior; TA relaxation) or plantarflexor (soleus; SOL relaxation) in response to an auditory stimulus. Single- and paired-pulse transcranial magnetic stimulation (TMS) was delivered to the hand area of the left M1 at different time intervals before and after the onset of TA or SOL relaxation. Motor evoked potentials (MEPs) were recorded from the right extensor carpi radialis (ECR) and flexor carpi radialis (FCR). MEP amplitudes of ECR and FCR caused by single-pulse TMS temporarily decreased after TA and SOL relaxation onset, respectively, as compared with those of the resting control. Furthermore, short-interval intracortical inhibition (SICI) of ECR evaluated with paired-pulse TMS temporarily increased after TA relaxation onset. Our findings indicate that muscle relaxation of the dorsiflexor reduced corticospinal excitability of the ipsilateral hand muscles. This is most likely caused by an increase in intracortical inhibition.

Somato-motor inhibitory processing in humans: evidence from neurophysiology and neuroimaging

Motor execution processing has been examined using an index of behavioral performance such as reaction times, kinetics, and kinematics. However, difficulties have been associated with the study of motor inhibitory processing because of the absence of actual behavioral performance. Therefore, non-invasive neurophysiological and neuroimaging methods including electroencephalography, magnetoencephalography, transcranial magnetic stimulation, and functional magnetic resonance imaging have been used to investigate neural processes in the central nervous system. We mainly reviewed research on somato-motor inhibitory processing based on data obtained by using these techniques, which can examine 'when', 'where, and 'how' motor inhibition occurs in the brain. Although to date a number of studies have used these techniques separately, few studies have utilized them in a comprehensive manner. In this review, we provide evidence that combining neurophysiological and neuroimaging methods should contribute to our understanding of how executive and inhibitory functions are implemented.

Influence of consonant voicing characteristics on sentence production in abductor versus adductor spasmodic dysphonia

OBJECTIVES/HYPOTHESIS

This study evaluated the hypotheses that sentence production by speakers with adductor (AD) and abductor (AB) spasmodic dysphonia (SD) may be differentially influenced by consonant voicing and manner features, in comparison with healthy, matched, nondysphonic controls.

STUDY DESIGN

This was a prospective, single blind study, using a between-groups, repeated measures design for the independent variables of perceived voice quality and sentence duration.

METHODS

Sixteen subjects with ADSD and 10 subjects with ABSD, as well as 26 matched healthy controls produced four short, simple sentences that were systematically loaded with voiced or voiceless consonants of either obstruant or continuant manner categories. Experienced voice clinicians, who were "blind" as to speakers' group affixations, used visual analog scaling to judge the overall voice quality of each sentence. Acoustic sentence durations were also measured.

RESULTS

Speakers with ABSD or ADSD demonstrated significantly poorer than normal voice quality on all sentences. Speakers with ABSD exhibited longer than normal duration for voiceless consonant sentences. Speakers with ADSD had poorer voice quality for voiced than for voiceless consonant sentences. Speakers with ABSD had longer durations for voiceless than for voiced consonant sentences.

CONCLUSIONS

The two subtypes of SD exhibit differential performance on the basis of consonant voicing in short, simple sentences; however, each subgroup manifested voicing-related differences on a different variable (voice quality vs sentence duration). Findings suggest different underlying pathophysiological mechanisms for ABSD and ADSD. Findings also support inclusion of short, simple sentences containing voiced or voiceless consonants as part of the diagnostic protocol for SD, with measurement of sentence duration in addition to judments of voice quality severity.

Abnormal movement preparation in task-specific focal hand dystonia

Electrophysiological and behavioral studies in primary dystonia suggest abnormalities during movement preparation, but this crucial phase preceding movement onset has not yet been studied specifically with functional magnetic resonance imaging (fMRI). To identify abnormalities in brain activation during movement preparation, we used event-related fMRI to analyze behaviorally unimpaired sequential finger movements in 18 patients with task-specific focal hand dystonia (FHD) and 18 healthy subjects. Patients and controls executed self-initiated or externally cued prelearnt four-digit sequential movements using either right or left hands. In FHD patients, motor performance of the sequential finger task was not associated with task-related dystonic posturing and their activation levels during motor execution were highly comparable with controls. On the other hand reduced activation was observed during movement preparation in the FHD patients in left premotor cortex / precentral gyrus for all conditions, and for self-initiation additionally in supplementary motor area, left mid-insula and anterior putamen, independent of effector side. Findings argue for abnormalities of early stages of motor control in FHD, manifesting during movement preparation. Since deficits map to regions involved in the coding of motor programs, we propose that task-specific dystonia is characterized by abnormalities during recruitment of motor programs: these do not manifest at the behavioral level during simple automated movements, however, errors in motor programs of complex movements established by extensive practice (a core feature of FHD), trigger the inappropriate movement patterns observed in task-specific dystonia.

Striatal dopaminergic dysfunction at rest and during task performance in writer's cramp

Writer's cramp is a task-specific focal hand dystonia characterized by involuntary excessive muscle contractions during writing. Although abnormal striatal dopamine receptor binding has been implicated in the pathophysiology of writer's cramp and other primary dystonias, endogenous dopamine release during task performance has not been previously investigated in writer's cramp. Using positron emission tomography imaging with the D2/D3 antagonist 11C-raclopride, we analysed striatal D2/D3 availability at rest and endogenous dopamine release during sequential finger tapping and speech production tasks in 15 patients with writer's cramp and 15 matched healthy control subjects. Compared with control subjects, patients had reduced 11C-raclopride binding to D2/D3 receptors at rest in the bilateral striatum, consistent with findings in previous studies. During the tapping task, patients had decreased dopamine release in the left striatum as assessed by reduced change in 11C-raclopride binding compared with control subjects. One cluster of reduced dopamine release in the left putamen during tapping overlapped with a region of reduced 11C-raclopride binding to D2/D3 receptors at rest. During the sentence production task, patients showed increased dopamine release in the left striatum. No overlap between altered dopamine release during speech production and reduced 11C-raclopride binding to D2/D3 receptors at rest was seen. Striatal regions where D2/D3 availability at rest positively correlated with disease duration were lateral and non-overlapping with striatal regions showing reduced D2/D3 receptor availability, except for a cluster in the left nucleus accumbens, which showed a negative correlation with disease duration and overlapped with striatal regions showing reduced D2/D3 availability. Our findings suggest that patients with writer's cramp may have divergent responses in striatal dopamine release during an asymptomatic motor task involving the dystonic hand and an unrelated asymptomatic task, sentence production. Our voxel-based results also suggest that writer's cramp may be associated with reduced striatal dopamine release occuring in the setting of reduced D2/D3 receptor availability and raise the possibility that basal ganglia circuits associated with premotor cortices and those associated with primary motor cortex are differentially affected in primary focal dystonias.

Patterns of muscle activity for digital coarticulation

Although piano playing is a highly skilled task, basic features of motor pattern generation may be shared across tasks involving fine movements, such as handling coins, fingering food, or using a touch screen. The scripted and sequential nature of piano playing offered the opportunity to quantify the neuromuscular basis of coarticulation, i.e., the manner in which the muscle activation for one sequential element is altered to facilitate production of the preceding and subsequent elements. Ten pianists were asked to play selected pieces with the right hand at a uniform tempo. Key-press times were recorded along with the electromyographic (EMG) activity from seven channels: thumb flexor and abductor muscles, a flexor for each finger, and the four-finger extensor muscle. For the thumb and index finger, principal components of EMG waveforms revealed highly consistent variations in the shape of the flexor bursts, depending on the type of sequence in which a particular central key press was embedded. For all digits, the duration of the central EMG burst scaled, along with slight variations across subjects in the duration of the interkeystroke intervals. Even within a narrow time frame (about 100 ms) centered on the central EMG burst, the exact balance of EMG amplitudes across multiple muscles depended on the nature of the preceding and subsequent key presses. This fails to support the idea of fixed burst patterns executed in sequential phases and instead provides evidence for neuromuscular coarticulation throughout the time course of a hand movement sequence.

Dystonia in childhood: clinical and objective measures and functional implications

Dystonia is a complex movement disorder that is challenging to identify and quantify. The aim of this article is to review the clinical scales, kinematic measures, and functional implications of dystonia. Clinical measures include the Barry-Albright Dystonia Scale, the Burke-Fahn-Marsden Movement Scale, the Unified Dystonia Rating Scale, the Global Dystonia Rating Scale, and the Movement Disorder-Childhood Rating Scale. The evidence, reliability, and validity of each scale will be outlined. The Hypertonia Assessment Tool will be discussed emphasizing the importance of discriminating hypertonia. The role of kinematic measures in analyzing dystonia will be explored, as well as the potential for its future clinical applications.

Contribution of intracortical inhibition in voluntary muscle relaxation

Terminating a voluntary muscle contraction is an important aspect of motor control, and yet, its neurophysiology is unclear. The objective of this study was to determine the role of short-interval intracortical inhibition (SICI) by comparing SICIs during relaxation from a power grip versus during a sustained power grip at the matching muscle activity level. Right-handed healthy young adults gripped and relaxed from power grip following auditory cues. The relaxation period was determined as the time for the flexor digitorum superficialis (FDS) muscle to reach its pre-contraction baseline level after the cue to relax. SICI during relaxation was obtained at different times into the relaxation period in two separate studies (70, 80, 90 % into relaxation in Study 1; 25, 50, 75 % into relaxation in Study 2). In addition, SICI during sustained contraction was assessed while subjects maintained a power grip at the matching FDS EMG levels (obtained during relaxation, for both Studies). Results showed that the mean SICI was greater during relaxation than during sustained contraction at the matching muscle activity level in both Studies (p < 0.05), indicating increased activation of intracortical inhibitory circuits for muscle relaxation. SICI gradually increased from 25 to 50 and 75 % into relaxation (Study 2, p < 0.05), but did not change from 70 to 80 and 90 % into relaxation (Study 1). MEP decreased with progression of relaxation (p < 0.05) in both Studies, reflecting gradual decreases in corticomotor excitability. This work supports the hypothesis that relaxation from a voluntary muscle contraction involves inhibitory activity in the primary motor cortex.

The differential modulation of the ventral premotor-motor interaction during movement initiation is deficient in patients with focal hand dystonia

A major feature of focal hand dystonia (FHD) pathophysiology is the loss of inhibition. One inhibitory process, surround inhibition, for which the cortical mechanisms are still unknown, is abnormal in FHD. As the ventral premotor cortex (PMv) plays a key role in the sensorimotor processing involved in shaping finger movements and has many projections onto the primary motor cortex (M1), we hypothesized that the PMv-M1 connections might play a role in surround inhibition. A paired-pulse transcranial magnetic stimulation paradigm was used in order to evaluate and compare the PMv-M1 interactions during different phases (rest, preparation and execution) of an index finger movement in patients with FHD and controls. A sub-threshold conditioning pulse (80% resting motor threshold) was applied to the PMv at 6 ms before M1 stimulation. The right abductor pollicis brevis, a surround muscle, was the target muscle. In healthy controls, the results showed that PMv stimulation induced an ipsilateral ventral premotor-motor inhibition at rest. This cortico-cortical interaction changed into an early facilitation (100 ms before movement onset) and turned back to inhibition 50 ms later. In patients with FHD, this PMv-M1 interaction and its modulation were absent. Our results show that, although the ipsilateral ventral premotor-motor inhibition does not play a key role in the genesis of surround inhibition, PMv has a dynamic influence on M1 excitability during the early steps of motor execution. The impaired cortico-cortical interactions observed in patients with FHD might contribute, at least in part, to the abnormal motor command.

Cortical activities associated with voluntary movements and involuntary movements

Recent advance in non-invasive techniques including electrophysiology and functional neuroimaging has enabled investigation of control mechanism of voluntary movements and pathophysiology of involuntary movements in human. Epicortical recording with subdural electrodes in epilepsy patients complemented the findings obtained by the non-invasive techniques. Before self-initiated simple movement, activation occurs first in the pre-supplementary motor area (pre-SMA) and SMA proper bilaterally with some somatotopic organisation, and the lateral premotor area (PMA) and primary motor cortex (M1) mainly contralateral to the movement with precise somatotopic organisation. Functional connectivity among cortical areas has been disclosed by cortico-cortical coherence, cortico-cortical evoked potential, and functional MRI. Cortical activities associated with involuntary movements have been studied by jerk-locked back averaging and cortico-muscular coherence. Application of transcranial magnetic stimulation helped clarifying the state of excitability and inhibition in M1. The sensorimotor cortex (S1-M1) was shown to play an important role in generation of cortical myoclonus, essential tremor, Parkinson tremor and focal dystonia. Cortical myoclonus is actively driven by S1-M1 while essential tremor and Parkinson tremor are mediated by S1-M1. 'Negative motor areas' at PMA and pre-SMA and 'inhibitory motor areas' at peri-rolandic cortex might be involved in the control of voluntary movement and generation of negative involuntary movements, respectively.

Structural, functional and molecular imaging of the brain in primary focal dystonia--a review

Primary focal dystonias form a group of neurological disorders characterized by involuntary, sustained muscle contractions causing twisting movements and abnormal postures. The estimated incidence is 12-25 per 100,000. The pathophysiology is largely unclear but genetic and environmental influences are suspected. Over the last decade neuroimaging techniques have been applied in patients with focal dystonia. Using structural, functional and molecular imaging techniques, abnormalities have been detected mainly in the sensorimotor cortex, basal ganglia and cerebellum. The shared anatomical localisations in different forms of focal dystonia support the hypothesis of a common causative mechanism. The primary defect in focal dystonia is hypothesised in the motor circuit connecting the cortex, basal ganglia, and cerebellum. Imaging techniques have clearly enhanced current knowledge on the pathophysiology of primary focal dystonia and will continue to do so in the future.

Defective inhibition and inter-regional phase synchronization in pianists with musician's dystonia: an EEG study

Recent neurophysiological studies have associated focal-task specific dystonia (FTSD) with impaired inhibitory function. However, it remains unknown whether FTSD also affects the inhibition (INH) of long-term overlearned motor programs. Consequently, we investigated in a Go/NoGo paradigm the neural correlates associated with the activation (ACT) and inhibition of long-term overlearned motor memory traces in pianists with musician's dystonia (MD), a form of FTSD, during a relevant motor task under constraint timing conditions with multichannel EEG. In NoGo trials, the movement related cortical potentials showed a positive shift after the NoGo signal related to inhibition and was significantly smaller over sensorimotor areas in musicians with MD. Further, we observed an increase at 850-900 ms in the power of beta oscillations which was significantly weaker for the patient group. The role of the inter-electrode phase coupling in the sensorimotor integration of inhibitory processes turned out to be the most relevant physiological marker: the global phase synchronization during INH exhibited an increase between 230 and 330 ms and 7-8 Hz, increase which was significantly smaller for pianists with MD. This effect was due to a weaker phase synchronization between the supplementary motor cortex and left premotor and sensorimotor electrodes in patients. Thus, our findings support the hypothesis of a deficient phase coupling between the neuronal assemblies required to inhibit motor memory traces in patients with MD. EMG recorded from the right flexor pollicis longus muscle confirmed that patients with MD had a disrupted INH in NoGo trials.

Slow pre-movement cortical potentials do not reflect individual response to therapy in writer's cramp

OBJECTIVE

To investigate whether movement-related cortical potentials (MRCP) provide a physiological correlate that indicates the response to treatment in patients with writer's cramp.

METHODS

In 21 patients with writer's cramp, who underwent 4 weeks of limb immobilization followed by re-training for 8 weeks, we recorded MRCPs preceding a self-initiated brisk finger abduction movement. MRCP measurements of pre-movement activity were performed at baseline, after the end of immobilization and four and 8 weeks of re-training. We examined 12 controls, who received no intervention, twice 4 weeks apart.

RESULTS

Patients benefited from the therapeutical intervention (Zeuner et al., 2008). They showed no abnormalities of the MRCPs at baseline. In controls, MRCPs did not significantly change after 4 weeks. In patients, immobilization and re-training had no effect on MRCPs. There was no correlation between the severity of dystonic symptoms or the individual treatment response and MRCPs.

CONCLUSION

MRCPs are stable measures for interventional studies. However, they do not reflect clinical severity of dystonic symptoms or improvement after therapeutic interventions.

SIGNIFICANCE

This is the first study to investigate MRCPs in a large cohort of patients with writer's cramp compared to a control group at different time points. These potentials do not reflect the motor control disorder in patients with writer's cramp.

Effect of motion imagery to counter rest-induced suppression of F-wave as a measure of anterior horn cell excitability

OBJECTIVE

To test if motor imagery prevents the rest-induced suppression of anterior horn cell excitability.

METHODS

Ten healthy subjects underwent two separate experiments, each consisting of stimulating the median nerve 100 times and recording F-waves from abductor pollicis brevis (APB) in three consecutive sessions: (1) after muscle exercise to standardize the baseline, (2) after immobilization of APB for 3h and (3) after muscle exercise to check recovery. We instructed the subject to volitionally relax APB in experiment 1 (relaxation task), and to periodically simulate thumb abduction without actual movement in experiment 2 (imagery task).

RESULTS

F-wave persistence and amplitude declined after relaxation task and recovered quickly after exercise, but changed little with imagery task. F-wave latencies showed no change when analyzed individually. The frequency distribution of collective F-waves recorded from all subjects remained the same after relaxation task, but showed a shift toward longer latencies after imagery task.

CONCLUSIONS

Mental imagery without overt motor output suffices to counter the effect of sustained volitional muscle relaxation, which would, otherwise, cause a reversible reduction in anterior horn cell excitability.

SIGNIFICANCE

This finding documents the importance of central drive for spinal excitability, which affects F-wave studies of a paretic muscle.

Cortical control of muscle relaxation: A lateralized readiness potential (LRP) investigation

OBJECTIVE

We used the lateralized readiness potential (LRP) to investigate cortical mechanisms underlying the termination of muscle contraction. Active suppression and withdrawal of activation have been proposed as underlying mechanisms in isotonic and isometric relaxation.

METHODS

Experiment 1 investigated isotonic wrist extension/release from extension. Experiment 2 investigated isometric activation/relaxation of a pinch grip. Tasks were performed with left and right hands and cued auditorily at variable intervals. EEG was recorded from 128 electrodes and processed to derive the LRP timelocked to the onset and offset of muscle contraction.

RESULTS

LRPs for isotonic activation and relaxation were of identical amplitude at electrodes overlying the motor cortex, but differed at frontal locations due to higher amplitude re-afferent activity during activation. The isometric LRP was significantly smaller during relaxation than during activation, without differences in scalp distribution.

CONCLUSION

The LRP findings confirm differences between isotonic and isometric relaxation, which may be partly explained by the need to suppress a stretch reflex in the former condition. The presence of an LRP associated with isometric relaxation reveals active preparation in the motor cortex, indicating that muscle relaxation in the isometric task cannot be explained solely by withdrawal of activation.

SIGNIFICANCE

High-density LRP recordings isolate different cortical mechanisms underlying the termination of muscle contraction.

Task-specific focal hand dystonia with usage of a spoon

We describe a 30-year-old woman who suffered from an unusual task-specific focal hand dystonia, which dominantly occurred with use of a spoon; there were no other activities affected, except for mild writer's dystonia on same side. This is the first report of a spoon-related focal dystonia.

The yips in golf: multimodal evidence for two subtypes

PURPOSE

To determine whether a model of two subtypes of yips is supported by evidence from a range of physiological, behavioral, and psychological measures.

METHODS

Fifteen golfers who experience yips symptoms while putting (mean age 58.1 yr, SD 13.6 yr), and nine golfers with no yips symptoms (mean age 39.6 yr, SD 19.3 yr) were recruited. Participants completed a golf history questionnaire to determine their playing experience and the nature of any yips symptoms experienced. In experiment 1, participants performed a putting task while electromyographic data were recorded from the forearm flexors and extensors and biceps brachii, bilaterally. The task was performed in two sessions, under low-pressure and high-pressure experimental conditions. The high-pressure condition was intended to increase anxiety through the use of a monetary incentive, video-taping of performance, and the presence of a confederate who provided negative feedback. Participants' state of anxiety was assessed using a questionnaire before each of the experimental sessions. In experiment 2, participants completed a task that required the inhibition of an anticipated response. Their accuracy and ability to inhibit their response was determined.

RESULTS

The golfers who experienced yips could be categorized according to whether they reported mainly movement-related symptoms (Type I) or anxiety-related symptoms (Type II). The Type I group exhibited greater muscle activity during putting and greater errors and less inhibition of the anticipated response task. The Type II group exhibited greater changes in cognitive anxiety and normal performance of the anticipated response task.

CONCLUSION

This study provides evidence in support of two yips subtypes. Type I is related to impaired movement initiation and execution, whereas Type II is related to performance anxiety.

Oscillatory cortical activity related to voluntary muscle relaxation: Influence of normal aging

OBJECTIVE

In this study we aimed to investigate if there are age-related differences in cortical oscillatory activity induced by self-paced muscular pure relaxation in comparison with muscle contraction as reference movement.

METHODS

Event-related (de)synchronization (ERD/ERS) have been recorded related to voluntary muscle contraction and relaxation in 10 young and 10 elderly right-handed healthy subjects. The muscle relaxation task consisted in a voluntary relaxation of maintained wrist extension without any overt, associated muscle contraction. The muscle contraction task corresponded to a self-initiated brief wrist extension.

RESULTS

In elderly subjects compared to young ones, mu and beta ERD preceding muscular relaxation was more widespread, beginning significantly earlier over contralateral frontocentral and parietocentral regions (p<0.05) as well as over ipsilateral regions (p<0.05). The beta synchronization was significantly attenuated (p<0.05).

CONCLUSIONS

These results suggest an alteration of inhibitory motor systems and an altered post-movement somesthetic inputs processing with normal aging. These alterations were accompanied by compensatory mechanisms.

SIGNIFICANCE

These age-related alterations during different phases of muscle relaxation could participate to explain global sensorimotor slowing observed with normal aging.

What is the Bereitschaftspotential?

Since discovery of the slow negative electroencephalographic (EEG) activity preceding self-initiated movement by Kornhuber and Deecke [Kornhuber HH, Deecke L. Hirnpotentialänderungen bei Willkurbewegungen und passiven Bewegungen des Menschen: Bereitschaftspotential und reafferente Potentiale. Pflugers Archiv 1965;284:1-17], various source localization techniques in normal subjects and epicortical recording in epilepsy patients have disclosed the generator mechanisms of each identifiable component of movement-related cortical potentials (MRCPs) to some extent. The initial slow segment of BP, called 'early BP' in this article, begins about 2 s before the movement onset in the pre-supplementary motor area (pre-SMA) with no site-specificity and in the SMA proper according to the somatotopic organization, and shortly thereafter in the lateral premotor cortex bilaterally with relatively clear somatotopy. About 400 ms before the movement onset, the steeper negative slope, called 'late BP' in this article (also referred to as NS'), occurs in the contralateral primary motor cortex (M1) and lateral premotor cortex with precise somatotopy. These two phases of BP are differentially influenced by various factors, especially by complexity of the movement which enhances only the late BP. Event-related desynchronization (ERD) of beta frequency EEG band before self-initiated movements shows a different temporospatial pattern from that of the BP, suggesting different neuronal mechanisms for the two. BP has been applied for investigating pathophysiology of various movement disorders. Volitional motor inhibition or muscle relaxation is preceded by BP quite similar to that preceding voluntary muscle contraction. Since BP of typical waveforms and temporospatial pattern does not occur before organic involuntary movements, BP is used for detecting the participation of the 'voluntary motor system' in the generation of apparently involuntary movements in patients with psychogenic movement disorders. In view of Libet et al.'s report [Libet B, Gleason CA, Wright EW, Pearl DK. Time of conscious intention to act in relation to onset of cerebral activity (readiness-potential). The unconscious initiation of a freely voluntary act. Brain 1983;106:623-642] that the awareness of intention to move occurred much later than the onset of BP, the early BP might reflect, physiologically, slowly increasing cortical excitability and, behaviorally, subconscious readiness for the forthcoming movement. Whether the late BP reflects conscious preparation for intended movement or not remains to be clarified.

Cortical and spinal abnormalities in psychogenic dystonia

OBJECTIVE

The pathophysiology of psychogenic dystonia has not been examined, but a growing body of literature suggests that abnormal sensory input from repetitive movements can lead to plastic cortical changes. Reduced cortical and spinal inhibition is well documented in organic dystonia. We tested the hypothesis that aberrant sensory input associated with abnormal posture may cause similar abnormalities by testing patients with psychogenic dystonia.

METHODS

We assessed cortical and spinal inhibitory circuits and cortical activity associated with voluntary movement in 10 patients with clinically definite psychogenic dystonia, 8 patients with organic dystonia, and 12 age-matched healthy control subjects.

RESULTS

Three measures of cortical inhibition, resting short- and long-interval intracortical inhibition and cortical silent period, were reduced in both psychogenic dystonia and organic dystonia. Cutaneous silent period mediated by spinal circuitries was increased in psychogenic and organic dystonia. Forearm spinal reciprocal inhibition was reduced in psychogenic dystonia.

INTERPRETATION

Psychogenic and organic dystonia share similar physiological abnormalities. Previous findings of abnormal cortical and spinal excitability in organic dystonia may, in part, be a consequence rather than a cause of dystonia. Alternatively, these findings may represent endophenotypic abnormalities that predispose to both types of dystonia.

Rate of force production and relaxation is impaired in patients with focal hand dystonia

One factor, which may contribute to slowed movement in dystonia, is impairment in controlling the voluntary rate of motor output. This study examined the ability of patients with focal hand dystonia to rapidly turn force on and off at the wrist and elbow joints. Dystonic patients were slower than controls in rapidly turning on force from rest at both joints, passively relaxing force and rapidly reversing force output from a steady-state flexion contraction. Adding a preload did not improve the ability of dystonic subjects to rapidly turn on force. These results support the idea that dystonia is a disorder of impaired motor cortical activation, possibly due to basal ganglia dysfunction.

Botulinum toxin therapy of writer's cramp

The pathophysiology and management of writer's cramp is one of the most challenging amongst the various forms of focal dystonias. Frequently, the dystonic postures are confounded by compensatory muscle activity. Correct identification of target muscles for botulinum toxin (BT) injections determines the treatment success. The dosages of different preparations vary, with 1 unit of Botox roughly equalling 3.5 units of Dysport. Electromyographic guided injections yield better results and may also decrease the amount of toxin required. Weakness of target muscles interfering with other non-writing activities is a frequently encountered adverse effect. Studies have shown that BT is a safe long-term therapy option.

The effect of repetitive transcranial magnetic stimulation on dystonia: a clinical and pathophysiological approach

Dystonia is characterized by sustained muscle contraction, which frequently causes repetitive, twisting movements or abnormal posture. The precise pathophysiological mechanisms of dystonia are still unknown. Several studies did demonstrate that, although motor cortex hyperexcitability appears to be responsible for abnormal co-contraction and overflow to adjacent muscles, plasticity mechanisms and integrative sensorimotor processing are also likely to be involved in this condition. Current dystonia treatments are based on oral medication, injection of botulinum toxin and, in a low proportion of cases, bi-pallidal deep brain stimulation. However, treatment outcome is generally disappointing. A few researchers have reported the application of repetitive transcranial magnetic stimulation (rTMS) over the primary motor cortex or the premotor cortex, with the goal of decreasing motor cortex hyperexcitability. This article reviews all studies using this technique in dystonia and discusses rTMS therapeutic impact and its possible mechanisms of action in this indication. Currently, the premotor cortex seems to be the best target for rTMS in dystonia. Rather than merely reducing the hyperexcitability of the primary motor cortex, this technique's clinical benefit seems to result from modifications in plasticity and restoration of sensorimotor integration. The corollary technique for chronic rTMS is electrical cortical stimulation. Even though this new therapeutic tool may have therapeutic promise, more studies are required to confirm it. In particular, we need to broaden our knowledge of rTMS impact on the various forms of dystonia and to optimize target localization.

Two phases of the contingent negative variation in humans: Association with motor and mental functions

The question of the relationship between contingent negative variation and the mechanisms controlling motor and mental functions has received inadequate study. The aims of the present work were to investigate the relationship between the early and late phases of contingent negative variation and the state of motor and mental functions in patients with Parkinson's disease and to study the effects of levodopa on contingent negative variation. Patients with Parkinson's disease showed significant decreases in the amplitudes and areas of both phases of contingent negative variation as compared with subjects of similar age. Correlation analysis demonstrated a negative relationship between the extent of impairment of coordinatory muscle interactions and the amplitudes of both phases of this variation (p < 0.01). There was a positive relationship between the magnitudes of both phases and the state of mental functions, particularly memory (p < 0.05). Treatment of patients with Parkinson's disease with levodopa was followed by a significant increase in the late phase (p < 0.05). The results obtained here provide evidence for the important role of structures supporting both direct motor control and mental functions in forming both phases of contingent negative variation. The greater effect of levodopa on the late phase of contingent negative variation suggests that the efferent system of the basal ganglia has a greater role in generating the late phase than in organizing the early phase of the variation.

Cortical mechanisms of unilateral voluntary motor inhibition in humans

While motor control is very often a goal-oriented event, little is known about the mechanisms underlying the termination of motor performance. To investigate what type of cortical activation underlies the muscle relaxation required to terminate the act, we performed single- and double-pulse transcranial magnetic stimulation (TMS) studies during voluntary muscle relaxation in nine normal volunteers. Subjects maintained a weak isometric contraction of the right first dorsal interosseous muscle (FDI), and either increased the level of contraction (Contraction), terminated the contraction (Relaxation), or maintained it (No-go) depending on a visual cue. Motor evoked potentials (MEP) and the silent period (SP) were recorded from the FDI during motor activity. To measure intra-cortical inhibition (ICI), we also performed double-pulse TMS, applying subthreshold conditioning stimuli at interstimulus intervals of 2 ms. When single-pulse TMS was given just prior to muscle relaxation (-21 to -70 ms), the MEP was reduced while the SP was unchanged. Intra-cortical inhibition was smaller just prior to the muscle relaxation. Unilateral voluntary muscle relaxation may not be associated with activation of the intracortical inhibitory system, but rather with the possible excitation of the corticospinal system, which can inhibit motoneurons disynaptically. These findings suggest that multiple inhibitory mechanisms act in diverse ways to achieve motor inhibition.

Electroencephalographic spectral power in writer's cramp patients: evidence for motor cortex malfunctioning during the cramp

We investigated cortical activation as reflected in task-related spectral power (TRPow) changes in 8 writer's cramp patients during writing on a digital board and during isometric contraction and compared them to those of 8 age-matched healthy subjects. Scalp EEG was recorded over the contralateral primary sensorimotor area (SM1(c)), and from the ipsilateral sensorimotor area (SM1(i)). The electromyogram (EMG) was recorded from the Extensor Digitorum Communis (Extensor), Flexor Digitorum Superficialis (Flexor), and First Dorsal Interosseous (FDI) muscles. We analyzed (1) handwriting performance, (2) changes in the TRPow confined to alpha and beta band, and (3) the EMG spectral power during both tasks, writing and isometric contraction. During writing, all patients developed writer's cramp. The handwriting in writer's cramp patients was associated with significantly less reduction of the beta-range TRPow and lower frequency of the TRPow reduction compared to controls. No significant differences between patients and controls for the alpha band TRPow reduction during handwriting were observed. During writing, the patients showed higher EMG spectral power than the controls but this difference was at the border of significance. The present results indicate disorder in the motor execution system, in writer's cramp patients, associated with impaired functional beta-network state of the contra- and ipsilateral sensorimotor cortices, most probably due to inadequate modulation of the intracortical inhibition associated with writing.

Functional MRI in human motor control studies and clinical applications

Functional magnetic resonance imaging (fMRI) has been a useful tool for the noninvasive mapping of brain function associated with various motor and cognitive tasks. Because fMRI is based on the blood oxygenation level dependent (BOLD) effect, it does not directly record neural activity. With the fMRI technique, distinguishing BOLD signals created by cortical projection neurons from those created by intracortical neurons appears to be difficult. Two major experimental designs are used in fMRI studies: block designs and event-related designs. Block-designed fMRI presupposes the steady state of regional cerebral blood flow and has been applied to examinations of brain activation caused by tasks requiring sustained or repetitive movements. By contrast, the more recently developed event-related fMRI with time resolution of a few seconds allows the mapping of brain activation associated with a single movement according to the transient aspects of the hemodynamic response. Increasing evidence suggests that multiple motor areas are engaged in a networked manner to execute various motor acts. In order to understand functional brain maps, it is important that one understands sequential and parallel organizations of anatomical connections between multiple motor areas. In fMRI studies of complex motor tasks, elementary parameters such as movement length, force, velocity, acceleration and frequency should be controlled, because inconsistency in those parameters may alter the extent and intensity of motor cortical activation, confounding interpretation of the findings obtained. In addition to initiation of movements, termination of movements plays an important role in the successful achievement of complex movements. Brain areas exclusively related to the termination of movements have been, for the first time, uncovered with an event-related fMRI technique. We propose the application of fMRI to the elucidation of the pathophysiology of movement disorders, particularly dystonia, which exhibits involuntary co-contraction of agonist and antagonist muscles and manifests abnormal posture or slow repetition of movements.

Praying-induced oromandibular dystonia

We report on an unusual presentation of a task-specific focal oromandibular dystonia in a 47-year-old man of Turkish descent. His speech was affected exclusively while reciting Islamic prayers in Arabic language, which he otherwise did not speak.

Muscle relaxation is impaired in dystonia: A reaction time study

A simple visual reaction time (RT) paradigm was used to investigate whether the velocity of relaxation is impaired in dystonia. In 16 subjects with a clinical diagnosis of adult-onset focal, segmental or multifocal dystonia and in 15 age-matched normal controls, the relaxation reaction time (R-RT) and the contraction reaction time (C-RT) were compared across different tasks involving the flexor carpi radialis (FCR), biceps brachii (BB) and triceps brachii (TR) arm muscles. In normal controls, the latency of EMG termination (R-RT) was significantly shorter than the latency of electromyographic (EMG) onset (C-RT) in the BB and TR muscles, but not in the FCR muscle. In dystonic patients, the latency of EMG termination (R-RT) was significantly longer than the latency of EMG onset (C-RT) in the FCR and BB muscles. No significant difference of the C-RT was observed between patients and controls whereas the R-RT was prolonged significantly in the BB and TR muscles of patients with dystonia and almost significantly in the FCR muscle. This study indicates that muscle relaxation is abnormal in patients with focal (multifocal or segmental) dystonia. The impaired muscle relaxation may contribute to the longer overlap of agonist-antagonist activities (co-contraction) typically observed in dystonia and to the slowness of voluntary movement sequencing.

Task-specific plasticity of somatosensory cortex in patients with writer's cramp

Focal dystonias such as writer's cramp are characterized by muscular cramps that accompany the execution of specific motor tasks. Until now, the pathophysiology of focal dystonia remains incompletely understood. Recent studies suggest that the development of writer's cramp is related to abnormal organization of primary somatosensory cortex (SI), which in turn leads to impaired motor function. To explore contributions of SI on mechanisms of task specificity in focal dystonia, we investigated dynamic alterations in the functional organization of SI as well as sensory-motor gating for rest, left- and right-handed writing and brushing in writer's cramp patients and healthy controls. The functional organization of somatosensory cortex was assessed by neuromagnetic source imaging (151 channel whole-head MEG). In accordance with previous reports, distances between cortical representations of thumb and little finger of the affected hand were smaller in patients compared to healthy subjects. However, similar to healthy controls, patients showed normal modulation of the functional organization of SI as induced by the execution of different motor tasks. Both in the control subjects and patients, cortical distances between representations of thumb and little finger increased when writing and brushing compared to the resting condition. Although, cramps only occured during writing, no differences in the organization of SI were seen among motor tasks. Our data suggest that despite alterations in the organization of primary somatosensory cortex in writer's cramp, the capability of SI to adapt dynamically to different tasks is not impaired.

Jaw deviation dystonia evaluated by movement-related cortical potentials and treated with muscle afferent block

Jaw-deviation dystonia is characterized by the lateral shift of the mandible due to involuntary masticatory muscle contraction, causing difficulties in speech or mastication. We evaluated a patient with jaw-deviation dystonia by recording movement-related cortical potentials (MRCPs) and treated with muscle afferent block (MAB). MRCP associated with mandibular movements (mouth opening, closing, and left and right lateral movements) was recorded in the patient and ten age-matched healthy subjects. In the control subjects, the amplitude of Bereitschaftspotential (BP)/negative slope (NS') was significantly higher for left lateral movements than for the mouth closing. The cortical map of BP/NS' prior to mouth opening and closing showed symmetric distribution, whereas those of lateral movements showed a slight predominance in the ipsilateral hemisphere. The patient showed lower amplitude as compared with control subjects. The right lateral movement (homonymous task) showed task-specific markedly reduced potentials. After MAB by intramuscular injection of lidocaine and ethanol to the inferior head of the left lateral pterygoid muscle, the deviation abolished and severity in speech and mastication was significantly improved. This study suggests that jaw-deviation dystonia might have the same etiology as other focal dystonias.

Somatosensory Representation of the Digits and Clinical Performance in Patients with Focal Hand Dystonia

OBJECTIVE

The purpose of this study was to incorporate magnetoencephalography and clinical testing to describe differences in somatosensory organization and sensorimotor function of the hand in patients with focal hand dystonia, a target-specific disorder of voluntary movement that interferes with fine motor control during the performance of rapid, repetitive, skilled movements.

DESIGN

This descriptive study included prospective, quasi-experimental comparisons between groups.

RESULTS

Patients with focal hand dystonia demonstrated deficits in physical variables, sensory processing, and motor control when compared with age- and sex-matched controls. They also had altered patterns of firing (amplitude and latency integrated over time) and abnormal somatosensory representations on magnetoencephalography.

CONCLUSIONS

These study findings suggest that there are alterations in both somatosensory representation of the digits and clinical performance in patients with focal hand dystonia. Future studies to determine if alterations in the sensorimotor feedback loop contribute to the development of focal hand dystonia are indicated. If so, intervention strategies may need to include specific types of somatosensory retraining as part of the rehabilitation program for patients with focal hand dystonia.

Role of the somatosensory system in primary dystonia

The pathophysiology of dystonia is still not fully understood, but it is widely held that a dysfunction of the corticostriatal-thalamocortical motor circuits plays a major role in the pathophysiology of this syndrome. Although the most dramatic symptoms in dystonia seem to be motor in nature, marked somatosensory perceptual deficits are also present in this disease. In addition, several lines of evidence, including neurophysiological, neuroimaging and experimental findings, suggest that both motor and somatosensory functions may be defective in dystonia. Consequently, abnormal processing of the somatosensory input in the central nervous system may lead to inefficient sensorimotor integration, thus contributing substantially to the generation of dystonic movements. Whether somatosensory abnormalities are capable of triggering dystonia is an issue warranting further study. Although it seems unlikely that abnormal somatosensory input is the only drive to dystonia, it might be more correlated to the development of focal hand than generalized dystonia because local somesthetic factors are more selectively involved in the former than in the latter where, instead it seems to be a widespread deficit in processing sensory stimuli of different modality. Because basal ganglia and motor areas are heavily connected not only with somatosensory areas, but also with visual and acoustic areas, it is possible that abnormalities of other sensory modalities, such as visual and acoustic, may also be implicated in the pathophysiology of more severe forms of primary dystonia. Further studies have to be addressed to the assessment of the role of sensory modalities and their interaction on the pathophysiology of different forms of primary dystonia.

Movement-related cortical potentials before jaw excursions in oromandibular dystonia

Oromandibular dystonia is a neurological disorder characterized by involuntary contraction of masticatory and/or tongue muscles. Cortical negative shifts preceding voluntary movements called "movement-related cortical potentials" (MRCPs) reflect a central motor control process. Reduced amplitude of MRCPs has been reported in other types of dystonia. To elucidate whether the abnormality is observed also in oromandibular dystonia, we compared MRCPs associated with mandibular movements in 6 patients with this condition and in 8 normal subjects. Electroencephalograms (EEGs) were recorded from 11 electrodes, and electromyograms (EMGs) were recorded from the masseter muscle and the suprahyoid muscles. The subjects were asked to repeat mouth opening, closing, and left and right lateral mandibular excursions. MRCPs were obtained by averaging the EEG using the EMG onset as the trigger signal. In the patient group, MRCP amplitudes over central and parietal areas for mouth opening and lateral movements were significantly reduced compared to normal subjects. In normal controls, the MRCPs at mouth opening and closing were symmetrically distributed, whereas those at lateral movements showed predominance over the hemisphere ipsilateral to the direction of the movement. This laterality was lost in the patient group. These results suggest impaired cortical preparatory process for jaw movements in oromandibular dystonia.